The present invention relates to methods for transmitting data in a system in which a single or a plurality of computer distributed systems are interconnected through a gateway via communication line, and more particularly, to a method for transmitting data by which, in order to improve the expansibility of a system, information filtering operation is carried out, that is, the amount of data to be transmitted onto a communication line is decreased to remarkably save a communication quantity and the receiving operation of unnecessary data is suppressed to selectively receive only necessary data to thereby improve the processing efficiencies and data receiving performances of respective computers at the time of transmitting contents code data.
Conventionally, when it is desired to carry out data communication from a single computer distributed system via a communication line, data has been attached with a destination address for one-to-one communication or with a group address for broadcast communication. In this case, the group address has been set to indicate a single common address for a group of computers. Equipment connected between transmission lines (e.g., LANs), for example, a router (a gate having a path selecting function) or a gateway (a gate having an address converting function) has a function of data to the transmission lines selected based on the destination address attached to the data or of executing a transmission suppression function.
These equipment have a function of extracting only part of information on a transmission line and sending it to another transmission line, so-called filtering function. Selection of information to be extracted between the transmission lines is executed on the basis of the destination computer address attached to the data.
Meanwhile, there has been widely employed a communication system using contents code, wherein a contents code indicative of the contents of data is attached to the data and a data receiver side judges reception or non-reception of the data on the basis of the contents code. With respect to the contents code, data within the system are classified into layered data depending on the types of the data, and a sub-contents code defining, e.g., a data group in addition to the contents code is attached thereto, so that the receiver side first judges reception or non-reception of the data on the basis of the sub-contents code, identifies the type of the computer in the group on the basis of the contents code, and then finally determines the reception or non-reception of the data.
With regard to the layered contents code, however, such a communication system has not been realized yet that uses the contents code having multiplexed sub-contents codes.
One of solutions to realizing flexible expansion of a system is to employ contents code communication. In this method, a message is broadcast to all computers and each receiver side judges reception or non-reception of the message. Thus, when this method is applied to a wide range of large-scale computer distributed system, the method has had a problem that the amount of message to be transmitted becomes enormous and communication load becomes high.
Techniques about the communication system using the group address, router, bridge, gateway and contents code are disclosed in D. E. Comer, et al, "Internetworking With TCP/IP--Vol 11: Design, Implementation, and Internals", PRENTICE HALL, New Jersey, 1991, pp. 81-163.